Electric heating – Metal heating – By arc
Patent
1998-06-11
1999-11-16
Mills, Gregory
Electric heating
Metal heating
By arc
21912163, 21912178, B23K 2600
Patent
active
059862360
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an installation for working on a zone of the wall of a tube by means of a laser beam directed at said zone and moved to scan the zone.
By way of example, the work may comprise cutting, or welding, or surface treatment.
Numerous devices have been proposed for performing such work. Essentially, they comprise a laser beam generator, a working head that includes both means for focusing the laser beam and an outlet nozzle for the focused beam, a waveguide for guiding the laser beam from the generator to the working head, and means for moving the working head so that the laser beam travels over the zone to be worked.
In certain applications, the means for moving the working head comprise a support that carries the working head and that revolves so that the working head moves around the tube, e.g. to cut the tube or to butt weld two tubes together.
The support which carries the working head must therefore be positioned accurately relative to the tube so that the axis of rotation of the support has a position that is defined relative to the tube, and that coincides therewith, at least approximately.
Publication FR-A-2 704 166 describes an installation as defined in the preamble of claim 1, and in which the rotary support is mounted on a plate which is directly fixed on the tube, however that solution is inappropriate when the tube is subjected to motion and vibration while the work is taking place, which applies in particular to tubes making up a pipeline that is being laid at sea from a barge. When working with a laser beam, it is most harmful for vibrations of the tube to be transmitted to the working head and to the beam waveguide.
To make a pipeline at sea, tubes of transportable length, generally 10 meters (m) to 24 are welded together on the "laying ramp" of the barge. After a tube has been welded into place, the barge is advanced by the length of the tube, with a corresponding length of pipeline being laid behind the barge. The barge is held in place by anchor lines and it is moved by winches. It is naturally subjected to the motion of the sea and its position is not absolutely fixed during welding even though the position of the pipeline which rests on the sea bed is practically constant along its axis. Relative movement is therefore continuously taking place between the barge and the pipework in the axial direction of the pipework, and this also gives rise to vibration.
An object of the present invention is to position the rotary support carrying the working head accurately relative to the tube without tube vibration being transmitted to the working head and to the waveguide connecting said head to the laser beam generator.
According to the invention, this object is achieved by placing the apparatus on a stand which carries the working head support in rotary manner, and in housing the apparatus and its stand inside a container having openings through which the tube can pass and including means for being temporarily fixed to the tube, the container also carrying the control cabinet and the high frequency cabinet for the laser generator, whereby the rotary support is fixed to the tube only via the container whose mass together with that of its contents considerably damps the transmission of stresses from the tube to the working head and to the waveguide.
The absence of direct fixing between the tube and the rotary support of the head also presents the advantage of making it very easy to adapt the system to tubes of different diameters.
By placing the high control cabinet and the frequency cabinet for the laser generator as stationary items in the container where the stand carrying the generator is also stationary during welding, it is certain that the high frequency cable connecting the high frequency cabinet to the generator is not subjected to any mechanical stress during welding, which is very important.
The invention also relates to a particular preferred embodiment of the working head.
In this embodiment, the working head includes a chassis fixed firstly to said rotary
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Gainand Yves
Marechal Alain
Mas Jean-Paul
Bouygues Offshore
Mills Gregory
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